Elucidation of cytomegalovirus (CMV) infection and pathogenicity, using guinea pigs and monkeys as models for understanding human CMV infection, will be continued. Detailed study of guinea pig cytomegalovirus (GPCMV) pathogenesis has revealed two distinct phases of infection: primary infection, during which viremia and virus infection of various tissues can be demonstrated, and persistent infection, during which virus can be readily recovered from the salivary gland for a prolonged time period in the presence of high levels of circulating antibody. Transmission of virus by contact infection was demonstrated conclusively. Furthermore, preliminary data indicates evidence of virus in the placenta of female guinea pigs impregnated during primary infection. A high incidence of green monkey cytomegalovirus (GMCMV) antibody in rhesus monkeys was detected during preliminary screening studies for antibody-free animals. While developing IFA techniques, for a more sensitive assay of GMCMV antibody, it was observed that the procedure could also be applied for determining antibody to human CMV in human sera. The primary advantage of the newly developed method was the absence of non-specific nuclear fluorescence indicative of antibody by human CMV infection. Continuation of the above studies will emphasize transplacental transmission of GPCMV in guinea pigs and GMCMV in rhesus monkeys. Special efforts will be placed on detection of virus infection in fetuses and offspring. Analysis of cytomegalovirus pathogenicity in monkeys will be stressed and the role played by pre-existing antibody in the development of experimental infection in guinea pigs and monkeys will be explored in greater detail. BIBLIOGRAPHIC REFERENCES: Swack, N.S., Michalski, F.J., Baumgarten, A. and Hsiung, G.D. Indirect fluorescent antibody test for human cytomegalovirus infection in the absence of interfering immunoglobulin G receptors. Infect. Immun. (May 1977), in press. Hsiung, G.D., Choi, Y.C. and Hastings, K. Viremia following cytomegalovirus infection in guinea pigs. ASM meeting, May 1977.